For union delegates gathering in Brighton, sunshine glimmered on the Channel outside the annual TUC conference but the focus for many inside was on stormy developments elsewhere.

After a tough first year in power for Labour, two big spectres dominated the meeting: disappointment with Keir Starmer’s government, and the march of Nigel Farage’s Reform UK.

The prime minister’s unexpectedly far-reaching reshuffle had provoked union fears that Labour may temper its plan to boost workers’ rights in yet another pro-growth reset.

Business leaders are already sensing an opportunity: Britain’s economy is weak, inflation is rising, Rachel Reeves’s tax on employment in her first autumn budget has chilled the jobs market, and the prospect of further rises, in her second act on 26 November, are looming.

For many it was ironic that the union gathering was taking place while the London Underground was brought close to a standstill by striking RMT members. Meanwhile, Labour was entering a potentially fractious deputy leadership battle of the kind Starmer promised was only really a feature of the last Tory government.

Businesses reckon Angela Rayner’s resignation and the sacking of Justin Madders, the junior minister responsible for the workers’ rights legislation – both politicians have close links to the union movement – could remove obstacles, while Peter Kyle, the new business secretary, had a warm relationship with tech bosses in his old job.

For union leaders, however, Labour watering down its workers’ rights bill, after a string of measures in Starmer’s first year hitting the poorest in society – not least cuts to winter fuel and proposed disability benefit cuts – would be a red line.

Sharon Graham, the Unite general secretary, said: “I do not understand how a Labour government has been attacking some of poorest in our society … pensioners, the disabled … whilst leaving the super-rich totally untouched.

“What the hell are Labour doing?”

After a tough year, it would also be yet another own goal. Many felt that Starmer’s decision to remove Madders – who, in the bar of the Grand Hotel, was commiserated by union bosses – was a misstep that had provoked unnecessary headlines about a new internecine Labour battle and yet more broken promises.

“It does seem like they have shot themselves in the foot a few times. I think they’re running out of legs to shoot at the moment,” said Steve Wright, the general secretary of the Fire Brigades Union.

Most union leaders drew a link between Labour fulfilling its workers’ rights reforms and killing off ballooning support for Farage, with a message that reneging on another promise would play into Reform’s hands.

Paul Nowak, the TUC general secretary, used his conference address to tell the prime minister he must show he is on the side of workers, adding that “‘change’ still feels like a slogan and not a lived reality”.

“[Delivering the employment rights bill is] the best way to rebuild our communities hit hard by low pay and insecure work … the sort of communities Nigel Farage likes to say he represents,” he said.

Downing Street sought to play down the fears, saying that the government is committed to the policy.

Ed Miliband, the energy secretary, was dispatched to speak at a dinner for the TUC general council at Brighton’s Grand hotel. Bridget Phillipson, the education secretary, will also attempt to reassure unions on Tuesday in her keynote Brighton speech.

With the prospect of a rancorous Labour party conference later this month, most union leaders said they did not believe the government would weaken the policy substantially.

Mike Clancy, the general secretary of the Prospect trade union, said: “I can’t see them doing it. I think it would be politically untenable. Because that would confirm there was intent behind the changes in the business department, and it was to favour business over working people.”

However, sources close to Labour and the unions said that while the bill would become law, it was likely that key elements would be watered down or delayed in the implementation of the policy to appease worried businesses.

For many, the priority of the TUC conference was to send a message that workers cannot shoulder the burden for the sticky position Britain’s economy – and the public finances – finds itself in.

Motions pushing for Labour to adopt a wealth tax had huge support. On the sidelines, the new leader of the Green party, Zack Polanski, held a fringe meeting pushing for such a levy – highlighting how Starmer could risk losing support from his left flank as well as the right.

“Sadly, a year on, people do not see the change they voted for and expected,” said Matt Wrack, the general secretary of Nasuwt, the teachers’ union. “We have stagnating living standards in the face of a cost of living crisis and the super-rich have got ever richer,” he said.

“[We need] no more delays, no more broken promises … Millions are watching and our test is to fight for that change and deliver it.”